It is known that properly twisting a blade of a turbomachine rotor such as a compressor, turbine, fan, pump, etc., improved performance and efficiency can be obtained. However, optimizing a blade section design has generally required extensive aerodynamic test data from wind tunnel and engineering design time. The manufacturing cost of a so-designed sheet-metal fan thereof has generally been prohibitive, particularly in automotive applications. The current energy shortages and noise regulations have led the automotive industry and other sheet metal fan users to consider more efficient and often more expensive fans which consume less energy and generate less noise.